The Venus
Transit 2004

... Photos by Themes

Venus' Aureole

Quite a few observers of the Venus Transit remarked upon a rare
optical phenomenon which could be perceived at the moment of the
second and third contacts. However, unlike the infamous "Black Drop" effect, "Venus'
Aureole" could only be seen under very good observing conditions
and with excellent telescopes. It was described as a "ring of light"
along the perimeter of Venus' black disc and extending beyond the
solar limb. Some observers talked about "Venus' horns", stretching
outwards from the two points where Venus' disc intersected that of the
Sun.

This aureole was first described by the famous Russian natural
scientist Mikhail
Vasil'evich Lomonosov (1711 - 1765) in his "Apparition of
Venus on the Sun, as observed from the Imperial Saint-Petersburg
Academy of Sciences on May 26th, 1761". He correctly interpreted the
phenomenon as the refraction of the sunlight in an atmosphere
surrounding Venus and considered this as additional support of his
conviction that there are many other inhabitable worlds beyond the
Earth.

A fictive observer on the Moon would see the same phenomenon - an
"Earth Aureole" - when the Earth's disc progressively covers the Sun
at the time of a lunar eclipse. It is exactly for this reason that the
Moon appears very red during a total lunar eclipse: the only sunlight
that reaches the Moon when it is entirely inside the Earth's shadow is
that passing through the Earth's atmosphere which "removes" most of
the blue light.

The VT-2004 Photo Archive contains a good
number of photos, both from professional and amateur telescopes, that
show the aureole phenomenon at the beginning and at the end of the
Venus Transit. Some of these photos have been collected on this
thematic page.

Venus' Aureole at the Third
Contact

DOT Group
45-cm Dutch Open Telescope
G-band image
[Venus' atmosphere is visible as a bright, circular band
outside the solar disc. This remarkable effect is due to
refraction in the upper layers of Venus' atmosphere that
bends the transmitted sunlight in our direction. See also the DOT Egress
movie]
More information at this site.
June 8, 2004
La Palma, Spain

DOT Group
45-cm Dutch Open Telescope
Ca II K image
[Venus' atmosphere is visible as a bright, circular band
outside the solar disc. This remarkable effect is due to
refraction in the upper layers of Venus' atmosphere that
bends the transmitted sunlight in our direction. See also the DOT Egress
movie]
More information at this site.
June 8, 2004
La Palma, Spain